1. Field of the Invention
This invention relates to multilevel electronic circuits and in particular to a method and structure for interconnecting different conductor levels in a multilayer structure.
2. Description of Related Art
Advanced interconnections schemes for VLSI (Very Large Scale Integration) multilayer circuits have evolved to the use of copper as the wiring levels and polyimide as the insulators, thus giving the lowest possible conductivity and permitivity, i.e., low resistance and low capacitance. As this copper/polyimide technology has evolved, damascene has become the wiring method of choice. Damascene construction refers to the depositing and planarizing of an insulator, etching an insulator groove or trench to form the wiring structure, plating copper over the insulator structure to fill the groove, and then chemical-mechanical polishing the copper such that it is coplanar with the polyimide, creating the final copper in the polyimide structure. Damascene construction is described in U.S. Pat. No. 4,789,648, assigned to the assignee of the present invention, and which is hereby incorporated by reference. However, it has been found that a nitride layer such as silicon nitride is required over the copper/polyimide structure for multi-level structures in order to deposit the next polyimide layer. In essence, the thin nitride layer acts as an etch stop when etching polyimide, and as a passivation over the copper to minimize and/or eliminate copper oxidation.
In older generations of technologies, the formation of stacked vias, for example, a direct M3 to M1 connection, required an impact to ground rules, that is, the stacked vias required independent definition of all the via and wiring levels in between the levels required to be connected, and therefore, because of minimum image size and overlay, and the concern that the subsequent via had to be within the metal landing pad to eliminate an unwanted shorting region, the density is degraded when a stacked via is applied. Also, the stacked via required multiple wiring connection interfaces and thus, contact and via resistance were an issue. Finally, in order to get around these overlay issues, the stacked via may have required a separate masking level to insure ground rules were maintained.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for making a stacked through via without any additional masks.
It is another object of the present invention to provide a method for making a stacked through via without any additional interconnection resistance.
A further object of the invention is to provide a method for making a stacked through via without impact to ground rules.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.